Sound emitting apparatus



Patented Oct. 26, 1937 UNITED STATES PATENT FFQE SOUND EMITTINGAPPARATUS Application February 1, 1934, Serial No. 709,396 In GermanyJune 15, 1933 3 Claims.

The present invention relates to improvements in sound emittingapparatus for the transmission of signals in air or water. One of theobjects of the invention is to increase the efficiency in the operationof such apparatus. Another object is to improve the sound emitted bysuch apparatus, while still other objects reside in overcoming variousdisadvantages of prior art constructions as will appear from thefollowing detailed description, particularly when read in conjunctionwith the appended drawing in which:

Fig. 1 shows a load curve in dependence on the speed of a mechanicallytuned oscillatory system without the use of a condenser;

Fig. 2 shows a load curve also dependent on the speed of an oscillatorysystem but with the use of a condenser connected in series or inparallel with the system according to the known manner;

Fig. 4 is a load curve obtained with the present invention, while Figs,3, 5 and 6 show wiring diagrams according to the invention.

For transmitting sound signals in air or water use is made of soundemitting apparatus which consist substantially of a loud speakingtelephone which is fed by single phase alternating current. In order toimprove the efficiency of such sound emitters it is customary to tunethe mechanical natural frequency of the sound producing mechanicalsystem to the sound frequency or to excite the sound producer with analternating current whose frequency or alternating rate, depending onwhether the sound producer is polarized or not, corresponds with themechanical natural frequency of the diaphragm. This operation can bebest explained by a diagrammatic showing. The curve BC of Fig. 1designates the electric load reception of the sound emitter dependent onthe frequency n of the feeding alternating current or on the angularvelocity of the alternating current. This curve has a maximum value A ata certain frequency nr, and this resonance point A is the point withinAwhich the sound emitter is preferably operated.

Notwithstanding this measure, the electric generator for the productionof the alternating current is inefciently utilized, as the sound emitteralong forms an inductive load for the generator and thus requires thegenerator also to produce the wattless current portion. In order toover'- come this defect, conde-risers have already been interposed inthe circuit of the sound emitter.

In known arrangements, which operate With condensers in the circuit ofthe sound emitter for improving the load factor (see German Patent348,127) the condensers are so constructed that, in addition to thetuned mechanical system, a tuned electric circuit is also present. Theresult of coupling these two systems is that the load curve no longerhas a maximum value in the operative point of the emitter, as in thearrangement without condensers (Fig. 1), but two closely adjacentmaximum values which are grouped about the operative point A (Fig. 2).This variation of the load curve is intentionally striven for by theoriginators of the known devices for the purpose of expanding orbroadening the resonance point or crest of the curve and to improve theconstancy of the angular velocity of the generator. Although anexpansion of the curve form is obtained by the interposition of a seriesor parallel condenser, the desired increase in the constancy of theangular velocity does not take place. In addition, this constructionincurs the defect that as a result of the coupling between theelectrical and mechanical oscillatory circuits unforeseen Vibrating andquavering sounds arise which distort the character of the sound andimpair the sound effect. The following considerations will serve toconfirm the fact that an improvement in the lconstancy of the angularvelocity is not attained.

An emitter without condensers (Fig. 1) produces its greatest soundperformance in the point A of the load curve, for which reason inpractice it is generally operated at this point. However, if variationsin the angular Velocity now arise in the engine driving the generatorthatproduces the alternating current, which variations cause a frequencyvariation of the operative frequency nr, it can be seen from Fig. 1 thata decrease in angular velocity and a resulting change of frequency fromnr to n1 also takes off the load of the generator, which opposes thereduction in the angular velocity. An increase in the angular velocity,on Athe other hand, and the resulting change of frequency to n2 causesunloading of the generator and a further increase in the angularvelocity. Thus, the branch AB of the curve of Fig. 1 opposesvariation'in the angular velocity and thereby reduces the drop ofangular velocity, while the branch AC of the curve of Fig. 1 supports achange of the angular velocity and an increase thereof.

In the curve according to known arrangements as shown in Fig. 2, whichemploy condensers in the electric circuit, the same occurrence takesplace, but in the reverse direction, as the'operative point A does notlie at a crest of the curve but, as a result of the coupling of amechanical with an electrical oscillatory system, in a trough of thedouble-wave curve, so that at decreasing variation in the angularvelocity the branch AB shows an increase of load and therewith anincrease in the drop of angular velocity, while at increasing angularvelocity the branch AC is connected with an increase of load and therebywith an action which tends to decrease the angular velocity.

In practice increasing as well as decreasing variations of angularvelocity arise in the same degree. The curve in Fig. 2 is also attainedonly when concordance, that is, resonance, exists between the mechanicalsound producer and the electrical oscillatory system. consisting ofInachine self-inductance, emitter self-inductance and condenser.However, just in this condition the emitter is easily affected by theenergy stored up in the electrical oscillatory circuit, so that, as afurther defect, vibrations arise in the emitter sounds, corresponding tothe diiference in the electrical and mechanical coupling frequency pointB and C. The emitter sound is then superimposed or accompanied by a lowfrequency, while the load amplitude fluctuates periodically. Theconstructional elements of the emitter are easily subject to excessstrain whichV may result in injury to the emitter.

In another known apparatus, in which the sound producer is excited by astatic frequency transformer, condensers and choke coils of certaindimensions are interposed in the circuit of the sound emitter, in orderto make certain paths permeable only for the basic frequency of thefeeding alternating current and other current paths only for an upperfrequency (harmonic) of the alternating current (see British Patent297,092). The load curve is hereby likewise unfavorably influenced, asit is dependent on the saturation of the static frequency transformer aswell as o-n the chokes,` etc. also present in the electric circuit. Theoriginators of this known arrangement never recognized the influence andimportance of the load curve.

The invention, on the contrary, is based on the correct knowledge of thesignificance which the course or form of the load curve has for thesound emitting apparatus. The object ofthe invention is to construct asound emitting apparatus having favorable properties relative to theform of its load curve aswell as with respect to the electric loadfactors. The invention thus relates to a sound emitting apparatusconsisting of a generator for alternating current of the frequency n, adiaphragm sound producer, whose mechanical oscillatory structure has anatural frequency equal to twice the frequency 11. of the alternatingcurrent supplied by the generator andY whose excitation coil is suppliedwith the alternating current of the frequency'u produced by thegenerator, and of an additional capacitative load of the generator forimproving the load factor, which is so dimensioned'that the curveindicating the electric load Vreception of the sound producer independency on the frequency, retains its characteristic single-waveform. at the operative point which it has` Without additionalcapacitative load.

According to one embodiment of theV invention as shown in Fig. 4, theintended effect is attained in that, with the use of a condenserconnected in parallel to thesound producer, the condenser C isdimensioned electrically so that the condition n2LC=1 is fulfilledbetween the self-inductance L of the emitter and the capacity C. Inthiscase it is seen that a load curve exactly like Fig. l is obtained, thusoffering the advantage that the load factor at the terminals of thegenerator equals l while the form of the curve remains neverthelessunchanged and the operative frequency lies accordingly at the crest orapex A o-f the curve. At the same time, the generator is loaded onlywith an operative load, inasmuch as in the case of resonance theapparent resistance of the condenser and of the emitter are equal,currents of equal magnitude flow in the emitter and condenser which,however, have a displacement ofY phase of 180, so that the generator hastherefore to furnish only the purely operative current.

, Examination of the load curve of the emitter outside of the operativeconditions at still higher frequency discloses that a second maximum asshown in Fig. 3 arises. This second maximum, at n3, results from thepotential resonance between the parallel connected self-inductance ofthe emitter plus the natural self-inductance of the generator and thecondenser connected parallel therewith. This second resonance has nounfavorable influence on the method of operation of the apparatus as itis far removed from the operative frequency of the emitter, and the formof the mechanical resonance frequency of the emitter is in no Waychanged by the second resonance apex. On the contrary, only by placingthe two resonances such a great distance from each other is it madepossible to avoid the variation of the load curve. At the same time, allVvibratory phenomena are hereby avoided,

Yand damage to the emitter will not occur.

The same effect maybe attained in a still more perfect/ manner by meansof the connection according to Fig. 5. Here the condenser C1 and theemitter inductance are first tuned to the operative frequency. By thisparallel connection the condenser plus the emitter thus act only as anohmic resistance. According to the invention the condenser C2 iselectrically dimensioned so that for the operative frequency it comes inresonance with the inductance of the generator G. Experiment has shownthat in this case also a resonance curve according to Fig. l isproduced.

However, the additional advantage is also obtained that the generator Gis loaded with rapidly increasing current, which produces a particularlyfavorable load in consideration of the reduced excitation of thealternating current generator. If

Yinstead of a stationary generator G use is made of a frequencytransformer, this last connection can be used to advantage, as the loadof a frequency transformerv can be greatly increased with a rapidlyincreasing load factor. In the foregoing connections for theV purposevof favorable tuning, the resonance circuits are also provided withtuning means (variable choke coils or the like)` as' shown in Fig. 6,in` order to make convenient manual adjustment possible.

I claim:

V1. Sound emitting apparatus consisting of a generator for alternatingcurrent, a tuned diaphragm sound producer Whose excitation winding issupplied with the Valternating current furnished by the generator, andan additional capacitative load of the generator connected in parallelto said excitation winding, said load being so dimensioned that thecurve indicating the electric load reception of the sound producerdependent on the frequency retains its characteristic single- Waveextent in the operative point, which extent said curve possesses withoutsaid additional capacitatiVe load.

2. Sound emitting apparatus according to claim 1, said capacitative loadcomprising a condenser, the capacity C of said condenser being sodimensioned that it complies, together with the inductivity L of theexcitation Winding of the emitter, with the resonance requirementn2LC=1.

3. Sound emitting apparatus according to claim 1, said oapacitative loadcomprising a condenser being so dimensioned that it complies, togetherwith the inductivity L of the excitation Winding of the emitter, withthe resonance requirement 1L2LC= 1, and a second condenser connected inseries with the generator and said parallel connection of said rstcondenser with said excitation Winding of the transmitter, said secondcondenser, together With the inductivty of the generator, being tuned tothe frequency of the generator.

ERNST WILCKENS.

